1. Field
The present invention relates generally to wireless charging, and more specifically to devices, systems, and methods related to wireless chargers.
2. Background
Typically, each battery powered device such as a wireless communication device (e.g. a cell-phone) requires its own charger and power source, which is usually the AC power outlet. This becomes unwieldy when many devices need charging, each requiring its own separate charger.
Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device to be charged. Such approaches generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and a receive antenna on the device to be charged. The receive antenna collects the radiated power and rectifies the radiated power for charging the battery. Antennas are generally of resonant length in order to improve the coupling efficiency. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas, so charging over reasonable distances (e.g., less than 1 to 2 meters) becomes difficult. Additionally, because the transmitting system radiates plane waves, unintentional radiation may interfere with other systems if not properly controlled through filtering.
Other approaches to wireless energy transmission techniques are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” device, mat, or surface and a receive antenna (plus a rectifying circuit) embedded in the host electronic device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g., within thousandths of meters). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically very small and requires the user to accurately locate the devices to a specific area. In addition, it is desirable to control the timing of the transmission and performance of the charger according to user preferences.